View previous topic :: View next topic 
Author 
Message 
David Bryant
Joined: 29 Jul 2005 Posts: 559 Location: Denver, Colorado

Posted: Wed Oct 05, 2005 4:48 pm Post subject: "Very Hard" puzzle for Wednesday, 5 October 


I thought this puzzle was even tougher than the usual "very hard" puzzle on this site. Great puzzle, Sam! dcb 

Back to top 


jess Guest

Posted: Thu Oct 06, 2005 4:58 am Post subject: 


it is really hard and I don't know. Who knows the answer and paste it here? 

Back to top 


jess Guest

Posted: Thu Oct 06, 2005 5:17 am Post subject: 


i suck here
x79 x4x 263
xx2 7x9 x4x
5xx xxx 879
xxx x7x 3xx
9xx 8x6 xx7
7x8 x5x xxx
xx7 xxx xx2
21x 4xx 7xx
69x x27 x3x
who can help me to solve it? 

Back to top 


amy Guest

Posted: Thu Oct 06, 2005 5:27 am Post subject: the answer of October 5 


jess wrote:  it is really hard and I don't know. Who knows the answer and paste it here? 
879 541 263
362 789 145
541 263 879
156 972 384
934 816 527
728 354 691
487 635 912
213 498 756
695 127 438 

Back to top 


jess Guest

Posted: Thu Oct 06, 2005 5:33 am Post subject: 


amy,
can u show me how to solve it? 

Back to top 


geoff h
Joined: 07 Aug 2005 Posts: 58 Location: Sydney

Posted: Thu Oct 06, 2005 1:59 pm Post subject: 


Hi Jess,
Firstly, a bit of housekeeping. You can quickly place Nr 8 in r9c9 as this is only possibility for 8 in Row 9. Also, I assume you have identified there is a pair of 1,5 in Row 2 ( r2c7 and r2c9 ). Also, there is a pair of 1,5 in Column 4 ( r1c4 and r9c4 ).
Now, for some hints;
1. Nr 8 then can quickly be placed in r4c8 as this is only possibility for 8 in Row 4. Also, Nr 9 can be placed in r4c4 as only possibility for 9 in Row 4.
2. There is a triplet of 1,4,5 in Column 7 ( r2c7, r5c7 and r9c7 ). This means you can eliminate all other 1,4,5s in Column 7 and means you have a pair of 6,9 in r6c7 and r7c7.
3. You can then place Nr 4 in r9c7 as this is the only possibility for Nr 4 in Box Nr 9. You can then easily complete Row 9 and solve the puzzle from there.
Hope this helps.
Cheers. 

Back to top 


BOB W Guest

Posted: Thu Oct 06, 2005 7:23 pm Post subject: 5 OCT Very Hard Puzzle 


Geoff H  Thanks for the tips, BUT  I don't understand why r9c7 must be a 4. Could you explain, please? Great hobby!!! Thanks
Love Sydney  visited in Nov 1999. 

Back to top 


geoff h
Joined: 07 Aug 2005 Posts: 58 Location: Sydney

Posted: Thu Oct 06, 2005 9:55 pm Post subject: 


Hi Bob,
Yes, Sydney sure is a great place to live!!
As you probably know, Box Nr 9 is the bottom box on the far right ( cell numbers r7c7  r9c9). When considering Box Nr 9, the only place where you can place a 4 is in r9c7. You can't place it in r7c8 or r8c8 because there is already a 4 in r2c8. You can't place it in r8c9 because there is already a 4 in r8c4. And finally, you can't place it in r7c7 because we have already eliminated Nrs 1,4,5 from that cell due to the triplet of 1,4,5 I mentioned in previous answer.
Cheers. 

Back to top 


David Bryant
Joined: 29 Jul 2005 Posts: 559 Location: Denver, Colorado

Posted: Thu Oct 06, 2005 10:22 pm Post subject: Re: 5 OCT Very Hard Puzzle 


BOB W wrote:  Geoff H  Thanks for the tips, BUT  I don't understand why r9c7 must be a 4. Could you explain, please? Great hobby!!! Thanks
Love Sydney  visited in Nov 1999. 
Just to be sure this is clear, here's a picture of the way the puzzle stands after applying Geoff's explanation  I've indicated the possibilities in column 7, for clarity.
Code: 
. 7 9 . 4 . 2 6 3
. . 2 7 . 9 1/5 4 .
5 . . . . . 8 7 9
. . . 9 7 . 3 8 .
9 . . 8 . 6 1/4/5 . 7
7 . 8 . 5 . 6/9 . .
. . 7 . . . 6/9 . 2
2 1 . 4 . . 7 . .
6 9 . . 2 7 1/4/5 3 8 
Concentrate on the bottom right 3x3 box. There must be a "4" in this box. It can't go in r7c7  that's either a "6" or a "9". It can't go in r7c8 or r8c8 because of the "4" at r2c8. And it can't go in r8c9 because of the "4" at r8c4. The only spot left for the "4" is r9c7.
This was the "Aha!" moment in this puzzle for me, but I spotted a different pattern  I hadn't yet noticed the {6, 9} pair on which Geoff relied. Looking at column 1, the only missing values are {1, 3, 4, 8}  since the values {3, 8} appear in row 4, it's clear that r4c1 must be either a "1" or a "4".
Since there can't be a "4" at r8c9 (because of the "4" at r8c4), the "4" in column 9 must appear in either r4c9 or r6c9. But this means there cannot be a "4" in either r5c7 or r5c8 ... since there can't be a "4" at r5c5 either (because of the "4" at r1c5) we see that the "4" in row 5 must either be at r5c2 or r5c3. But that means we can eliminate the possibility of a "4" at r4c1, so that r4c1 = 1 ... this quickly leads to a "1" at r3c3. It also implies that r7c1 = 4 (since "4" can't go at r1c1 or r2c1), and this means that r9c7 = 4 (since the "4" in the bottom right 3x3 box now has to fit in row 9). dcb 

Back to top 


jambon_vn
Joined: 06 Oct 2005 Posts: 2

Posted: Thu Oct 06, 2005 11:56 pm Post subject: Re: 5 OCT Very Hard Puzzle 


David Bryant wrote: 
Concentrate on the bottom right 3x3 box. There must be a "4" in this box. It can't go in r7c7  that's either a "6" or a "9". It can't go in r7c8 or r8c8 because of the "4" at r2c8. And it can't go in r8c9 because of the "4" at r8c4. The only spot left for the "4" is r9c7.

Can you explain why you can get the solution after having nr 4 in r9c7?
Quote: 
This was the "Aha!" moment in this puzzle for me, but I spotted a different pattern  I hadn't yet noticed the {6, 9} pair on which Geoff relied. Looking at column 1, the only missing values are {1, 3, 4, 8}  since the values {3, 8} appear in row 4, it's clear that r4c1 must be either a "1" or a "4".
Since there can't be a "4" at r8c9 (because of the "4" at r8c4), the "4" in column 9 must appear in either r4c9 or r6c9. But this means there cannot be a "4" in either r5c7 or r5c8 ... since there can't be a "4" at r5c5 either (because of the "4" at r1c5) we see that the "4" in row 5 must either be at r5c2 or r5c3. But that means we can eliminate the possibility of a "4" at r4c1, so that r4c1 = 1 ... this quickly leads to a "1" at r3c3. It also implies that r7c1 = 4 (since "4" can't go at r1c1 or r2c1), and this means that r9c7 = 4 (since the "4" in the bottom right 3x3 box now has to fit in row 9). dcb 
Really nice move. 

Back to top 


geoff h
Joined: 07 Aug 2005 Posts: 58 Location: Sydney

Posted: Fri Oct 07, 2005 1:41 am Post subject: 


After posting a 4 at r9c7, you can do the following steps;
1. Place Nr 5 at r9c3 because only possibilities in that cell are 4 or 5.
2. Then place Nr 1 at r9c4 because only possibilities in that cell are 1 or 5.
3. Then place Nr 3 at r8c3 because only possibilities in that cell are 3 or 5.
This then also gives you a pair of 4,8 in Row 7.
4. The the final major clue to solving this puzzle is to consider Row 5 and its interaction with Box Nr 4. Nr 4 has to appear in either r5c2 or r5c3 as these are the only places it can go in Row 5. Therefore, you can DELETE ALL OTHER 4s IN BOX NO.4. This then means you can place Nr 1 in r4c1 because the only possibilities for that cell are 1 and 4.
After that, it's plain sailing  I should leave the rest of the puzzle for you to solve yourself.
Cheers. 

Back to top 


jess Guest

Posted: Fri Oct 07, 2005 5:33 am Post subject: 


Hi, geoff
Thanks for explaining and I finially solve it since I can put the Nr 8. So thanks alot!! 

Back to top 


BOB W Guest

Posted: Fri Oct 07, 2005 8:05 pm Post subject: 5 OCT very hard puzzle 


Thank you Geoff and David for your kind help. 

Back to top 


Guest

Posted: Tue Oct 11, 2005 9:52 pm Post subject:  


I actually found this one to be quite easy, I am new to the forum, and have only been doing the Sudoku puzzles for about 2 weeks, if that, but I sat down and did this puzzle in maybe 1520min. Im not sure if that is good or not but that was the best time I have had on a very hard puzzle.
I would post how I did it but I am at school and need to get to my next class, maybe next time. And Hello everyone. 

Back to top 


Sahara Guest

Posted: Wed Oct 12, 2005 11:40 am Post subject: 


Many thanks for geoff h explanation. 

Back to top 


Guest

Posted: Wed Oct 12, 2005 2:02 pm Post subject: Re:  


Anonymous wrote:  I actually found this one to be quite easy, I am new to the forum, and have only been doing the Sudoku puzzles for about 2 weeks, if that, but I sat down and did this puzzle in maybe 1520min. Im not sure if that is good or not but that was the best time I have had on a very hard puzzle.
I would post how I did it but I am at school and need to get to my next class, maybe next time. And Hello everyone. 
You must be very very smart. 

Back to top 


Guest

Posted: Mon Nov 07, 2005 2:41 am Post subject: 


375 xxx xx6
x1x x62 8xx
xxx xxx 5x1
xxx x4x 76x
xxx 8x6 xxx
x68 x1x xxx
2x1 xxx xxx
xx3 15x x8x
9xx xxx 153
can anyone help my solve that one?? 

Back to top 


Louise56
Joined: 21 Sep 2005 Posts: 94 Location: El Cajon, California USA

Posted: Mon Nov 07, 2005 3:05 am Post subject: 


Anonymous wrote:  375 xxx xx6
x1x x62 8xx
xxx xxx 5x1
xxx x4x 76x
xxx 8x6 xxx
x68 x1x xxx
2x1 xxx xxx
xx3 15x x8x
9xx xxx 153
can anyone help my solve that one?? 
Hello!
First pencil in all the possibilities. A sole candidate (SC) is the only number that can be in a certain space. You will find:
4 SC in r2c1 (4 is the only number in row 2 column 1). Put a 4 there and erase 4's from that 3x3 box and from other spaces in r2 and c1.
4 SC in r7c2 (do the same clean up)
8 SC in r9c2
9 SC in r2c3
Keep going through the 3x3 boxes, each row and each column and look for spaces where a number is the sole candidate or all by itself. If you get stuck again write back. 

Back to top 


Guest Guest

Posted: Mon Nov 07, 2005 8:34 am Post subject: 5th Very Hard Puzzle 


jess wrote:  it is really hard and I don't know. Who knows the answer and paste it here? 
If you need to check your answer; you can see the solution from the day after the puzzle first appears  archives. I took two hours to solve it, (without using "ariadies thread" or any of the other "guess" or "trial and error" systems) 

Back to top 




You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum

Powered by phpBB © 2001, 2005 phpBB Group
